Rock crushers reduce the size of rocks in order to provide material for road beds, concrete, building foundations and the like. By definition, rock crushers need to be heavy duty to avoid breakage and bending during the crushing process. Rock crushers may be categorized as cone crushers, jaw crushers, and impact crusher, but this disclosure will focus on cone crushers. Cone crushers break up rocks and other hard material by squeezing or compressing it between convex and concave-shaped surfaces covered by hardened wear surfaces. Cone crushers are normally used as the second or third stage crusher, with a reduction ratio of from about 6 to 8 to 1. A typical cone crusher includes a conically-shaped head, which is part of an upper rock crusher assembly. The conical head both gyrates or oscillates and rotates relative to a stationary bowl that includes a hardened bowl liner. The spacing between the bowl liner and the cone at any given point opens and closes as the cone oscillates relative to and inside the bowl. Rocks are deposited in the spacing and the rocks slide down between these surfaces as the space opens, and the rocks are crushed as the space closes.
In this process of rock reduction, it is not uncommon for a large chunk of very hard rock, such as granite or basalt, or a piece of metal, sometimes called tramp iron, such as a tooth from a rock digging bucket, to enter the crusher. If the uncrushable material is larger than the maximum allowed size for passing through the cone crusher, such material can damage the crusher if there is no relief mechanism in place. Rock crushers typically accommodate these uncrushables through a mechanism known as tramp iron relief systems. For example, the bowl in a cone crusher is mounted relative to the cone at a desired fixed spacing. However, the upper assembly, including the bowl, is seated relative to the primary support structure so as to allow lifting of the bowl relative to the cone. The mounting mechanism further typically includes hydraulic clamping cylinders having pistons which serve to resist such lifting of the bowl. The clamping cylinders are pressurized to resistively hold the upper assembly and thus the bowl in place. When the resistance of the clamping cylinders is exceeded, at least one of the cylinder relief valves pops open and the upper assembly, including the bowl, will lift away from the cone and allow passage of the uncrushables. When one or more of the relief valves pops open, hydraulic oil typically flows to an adjacent accumulator. Once the uncrushable passes through the crusher, pressure in the cylinder is reduced, the relief valve reseats, oil flows back to the clamping cylinder from the accumulator, and the crusher is ready to operate. This process is normally very fast, taking no more than a few milliseconds.
The foregoing relief systems work reasonably well to protect cone crushers. However, given that fluid needs to flow from the clamping cylinders to the accumulators before pressure on the crusher is released, the relief might not be as quick as desired. The same is true as oil flows back to the clamping cylinders, and the crusher may not be ready to resume operation as quickly as it might otherwise if hydraulic fluid did not have to flow so far or in such quantity. Also, the accumulators are large, and because they should be positioned close to the cylinders, they may limit the number of clamping cylinders that can be utilized. This requires the bowl and/or the cone to be of heavier construction than might be the case if more cylinders were used or if the relief could be facilitated more quickly. This adds weight and cost to the entire crusher, and makes transporting the crusher more challenging than if it were able to be constructed somewhat lighter.